Thin-film light-emitting device including charge generating junction layer and method of fabricating thin-film light-emitting device

ABSTRACT

The present invention discloses a thin-film light-emitting device including a charge generating junction layer and a method of fabricating the thin-film light-emitting device. The thin-film light-emitting device including a charge generating junction layer according to one embodiment of the present invention includes a negative electrode; at least one light-emitting unit formed on the negative electrode and including a charge generating junction layer, an electron injection/transport layer, a thin-film light-emitting layer, and a hole injection/transport layer in a sequential order; and a negative electrode formed on the light-emitting unit. In the thin-film light-emitting device of the present invention, the charge generating junction layer has a layer-by-layer structure in which a p-type semiconductor layer and an n-type semiconductor layer are formed, and the concentration of oxygen vacancies at the interface between the p-type and n-type semiconductor layers is adjusted by annealing the n-type semiconductor layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional Application of U.S. application Ser.No. 16/759,556, filed on Apr. 27, 2020, which is a National Stage Entryof PCT International Application No. PCT/KR2018/000782, which was filedon Jan. 17, 2018, and which claims priority to Korean Patent ApplicationNo. 10-2017-0141177, filed on Oct. 27, 2017 in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein byreference.

BACKGROUND OF THE DISCLOSURE Field of the Disclosure

The present invention relates to a thin-film light-emitting deviceincluding a charge generating junction layer and a method of fabricatingthe thin-film light-emitting device, and more particularly, to athin-film (e.g., quantum dot or organic) light-emitting device includinga charge generating junction layer with improved power efficiency andcurrent efficiency and a method of fabricating the thin-filmlight-emitting device.

Description of the Related Art

A light-emitting device (LED) is a device using a phenomenon in whichlight is emitted while electrons and holes combine when current flowsthrough a diode formed of a gallium nitride (GaN)-based compoundsemiconductor, and has attracted great attention in various fields suchas optical devices and high power electronic devices.

In recent years, studies have been conducted to fabricatehigh-performance and long-lifespan thin-film (e.g., quantum dot ororganic) light-emitting devices. To realize this performance, injectionof charge, transport of injected charge, and generation of additionalcharge in a light-emitting device are very important considerations.

Accordingly, a charge generating junction layer serving to lower anenergy barrier was additionally formed inside a light-emitting device tofacilitate transfer of charge to the next transport layer.

However, a low-molecular-weight P-N junction layer used as the chargegenerating junction layer was formed only through a vacuum depositionprocess because the P-N junction layer was very difficult to form in theform of liquid.

However, when a large area display is manufactured using a vacuumdeposition process, a substrate or a mask may be warped, and a long tacktime (about 1 hour) is required to vaporize small molecules.Accordingly, there is a need for an easy method of fabricating alow-cost charge generating junction layer applicable to a large areaprocess.

In addition, among light-emitting devices, in the case of a tandemlight-emitting device fabricated by laminating two or morelight-emitting units, since the number of layers of each light-emittingunit is different, a process may be complicated. In addition, sincematerials used to form each light-emitting unit are different, materialcosts may be increased. In addition, since the number of layersincreases, a driving voltage may be increased, thereby reducingefficiency.

SUMMARY OF THE DISCLOSURE

Therefore, the present invention has been made in view of the aboveproblems, and it is one object of the present invention to provide athin-film light-emitting device including a charge generating junctionlayer consisting of an p-type semiconductor layer and an annealed n-typesemiconductor layer. According to the present invention, theconcentration of oxygen vacancies at the interface between the p-typeand n-type semiconductor layers may be adjusted, thereby improving powerefficiency and current efficiency.

It is another object of the present invention to provide a thin-filmlight-emitting device including a charge generating junction layerconsisting of p-type and n-type semiconductor layers formed using oxidesemiconductors. With this configuration, resistance to oxygen andmoisture may be increased, thereby increasing the lifespan of thedevice.

It is still another object of the present invention to provide athin-film light-emitting device including a charge generating junctionlayer consisting of p-type and n-type semiconductor layers. According tothe present invention, charge is generated at the interface between thep-type and n-type semiconductor layers, thereby stabilizing generationand injection of charge.

It is still another object of the present invention to provide athin-film light-emitting device including a charge generating junctionlayer. According to the present invention, the charge generatingjunction layer consisting of p-type and n-type semiconductor layers isformed using a solution process. Accordingly, process time may beshortened, and problems related to the work function of the upper orlower electrode of the thin-film light-emitting device may be solved.

It is yet another object of the present invention to provide a thin-filmlight-emitting device having a tandem structure. According to thepresent invention, a high-performance thin-film light-emitting devicemay be fabricated at low cost.

In accordance with one aspect of the present invention, provided is athin-film light-emitting device including a negative electrode; at leastone light-emitting unit formed on the negative electrode and including acharge generating junction layer, an electron injection/transport layer,a thin-film light-emitting layer, and a hole injection/transport layerin a sequential order; and a positive electrode formed on thelight-emitting unit, wherein the charge generating junction layer has alayer-by-layer structure in which a p-type semiconductor layer and ann-type semiconductor layer are formed, and a concentration of oxygenvacancies at an interface between the p-type and n-type semiconductorlayers is adjusted by annealing the n-type semiconductor layer.

The annealing treatment may increase a proportion of the p-typesemiconductor layer at the interface between the p-type and n-typesemiconductor layers.

The charge generating junction layer may be formed using a solutionprocess.

The thin-film light-emitting device may further include an auxiliarycharge generating junction layer on the light-emitting unit.

The annealing treatment may be performed at a temperature of 160° C. to250° C.

A thickness ratio of the p-type semiconductor layer to the n-typesemiconductor layer may be 1:1 to 1:5.

The p-type semiconductor layer may have a thickness of 1 nm to 50 nm.

The n-type semiconductor layer may have a thickness of 1 nm to 50 nm.

The p-type and n-type semiconductor layers may be formed using oxidesemiconductors.

The p-type semiconductor layer may include one or more of copper oxide(CuO) and copper oxide (CuO) doped with a first dopant.

The first dopant may include one or more of nickel (Ni), copper (Cu),lithium (Li), and zinc (Zn).

The first dopant may be included in an amount of 1 atomic % to 50 atomic% in the copper oxide (CuO).

The p-type semiconductor layer may include one or more of nickel oxide(NiO) and nickel oxide (NiO) doped with a second dopant.

The second dopant may include one or more of tin (Sn), copper (Cu),lithium (Li), and zinc (Zn).

The second dopant may be included in an amount of 0.1 atomic % to 50atomic % in the nickel oxide (NiO).

The n-type semiconductor layer may include one or more of zinc oxide(ZnO) and zinc oxide (ZnO) doped with a third dopant.

The third dopant may include one or more of cesium (Cs), lithium (Li),aluminum (Al), magnesium (Mg), indium (In), calcium (Ca), and gallium(Ga).

The third dopant may be included in an amount of 0.1 atomic % to 20atomic % in the zinc oxide (ZnO).

The light-emitting unit may be repeatedly laminated 1 to 5 times.

The thin-film light-emitting device may further include a reflectivelayer formed on the negative electrode.

The thin-film light-emitting device may further include a refractiveindex compensation layer formed on the positive electrode.

The thin-film light-emitting layer may be a quantum dot light-emittinglayer or an organic light-emitting layer.

In accordance with another aspect of the present invention, provided isa method of fabricating a thin-film light-emitting device, the methodincluding a step of forming a negative electrode on a substrate; a stepof forming at least one light-emitting unit on the negative electrode;and a step of forming a positive electrode on the light-emitting unit,wherein the step of forming the light-emitting unit includes a step offorming a charge generating junction layer on the negative electrode; astep of forming an electron injection/transport layer on the chargegenerating junction layer; a step of forming a thin-film light-emittinglayer on the electron injection/transport layer; and a step of forming ahole injection/transport layer on the thin-film light-emitting layer,wherein the charge generating junction layer has a layer-by-layerstructure in which a p-type semiconductor layer and an n-typesemiconductor layer are formed, and a concentration of oxygen vacanciesat an interface between the p-type and n-type semiconductor layers isadjusted by annealing the n-type semiconductor layer.

The charge generating junction layer may be formed using a solutionprocess.

The annealing treatment may be performed at a temperature of 160° C. to250° C.

The method may further include, after the step of forming thelight-emitting unit, a step of forming an auxiliary charge generatingjunction layer on the light-emitting unit.

A thin-film light-emitting device according to embodiments of thepresent invention includes a charge generating junction layer consistingof an p-type semiconductor layer and an annealed n-type semiconductorlayer. With this configuration, the concentration of oxygen vacancies atthe interface between the p-type and n-type semiconductor layers can beadjusted, thereby improving power efficiency and current efficiency.

The thin-film light-emitting device according to embodiments of thepresent invention includes a charge generating junction layer consistingof p-type and n-type semiconductor layers formed using oxidesemiconductors. With this configuration, resistance to oxygen andmoisture can be improved, thereby increasing the lifespan of the device.

The thin-film light-emitting device according to embodiments of thepresent invention includes a charge generating junction layer consistingof p-type and n-type semiconductor layers. With this configuration,charge is generated at the interface between the p-type and n-typesemiconductor layers, thereby stabilizing generation and injection ofcharge.

In the thin-film light-emitting device according to embodiments of thepresent invention, a charge generating junction layer consisting ofp-type and n-type semiconductor layers is formed using a solutionprocess. Accordingly, process time can be shortened, and problemsrelated to the work function of the upper or lower electrode ofthin-film light-emitting device can be solved.

According to the thin-film light-emitting device according to oneembodiment of the present invention, by forming a thin-filmlight-emitting device having a tandem structure, a high-performancethin-film light-emitting device can be fabricated at low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional view of a thin-film light-emitting deviceincluding a charge generating junction layer according to one embodimentof the present invention.

FIG. 1B is a cross-sectional view of a thin-film light-emitting deviceincluding a charge generating junction layer according to anotherembodiment of the present invention.

FIG. 2 illustrates the tandem structure of a thin-film light-emittingdevice according to one embodiment of the present invention.

FIGS. 3A and 3B are flowcharts for explaining a method of fabricating athin-film light-emitting device according to one embodiment of thepresent invention.

FIGS. 4A to 4H show the characteristics of a thin-film light-emittingdevice (control device) that does not include a solution process-basedcharge generating junction layer according to Comparative Example andthe characteristics of a thin-film light-emitting device including acharge generating junction layer (CGL device) according to Example 1 ofthe present invention.

FIGS. 5A to 5D show the characteristics of a thin-film light-emittingdevice including a charge generating junction layer according to Example1 of the present invention depending on the dopant concentrations of ap-type semiconductor layer.

FIGS. 6A to 6D show the characteristics of a thin-film light-emittingdevice including a charge generating junction layer according to Example1 of the present invention depending on the annealing temperatures of ann-type semiconductor layer.

FIGS. 7A to 7D show the characteristics of a thin-film light-emittingdevice including a charge generating junction layer according to Example1 of the present invention depending on the thicknesses of an n-typesemiconductor layer.

FIGS. 8A to 8D show the characteristics of a thin-film light-emittingdevice including a charge generating junction layer according to Example1 of the present invention depending on the thicknesses of an electroninjection/transport layer formed on the upper portion of a solutionprocess-based charge generating junction layer.

FIGS. 9A to 9C show the characteristics of a thin-film light-emittingdevice (w/o) that does not include an n-type semiconductor layer and thecharacteristics of a thin-film light-emitting device (w/) including acharge generating junction layer according to Example 1 of the presentinvention.

FIG. 10 is a graph showing the current-voltage characteristics of athin-film light-emitting device (PP:WOx/LZO CGJ) including a chargegenerating junction layer consisting of a p-type semiconductor layerincluding an organic substance and an n-type semiconductor layerincluding an oxide semiconductor and the current-voltage characteristicsof a thin-film light-emitting device (Li:CuO/LZO CGJ) including a chargegenerating junction layer according to Example 1 of the presentinvention.

FIGS. 11A to 11C show the characteristics of a top-emitting thin-filmlight-emitting device (a thin-film light-emitting device including acharge generating junction layer according to another embodiment of thepresent invention).

FIGS. 12A to 12F show the ultraviolet photoelectron spectroscopy spectraof a thin-film light-emitting device including a charge generatingjunction layer according to Example 1 of the present invention.

FIGS. 13A to 13D show the characteristics of a thin-film light-emittingdevice including an NPD/HAT-CN junction as a charge generating junctionlayer and the characteristics of a thin-film light-emitting deviceincluding a charge generating junction layer (Li:CuO/LiZnO) according toExample 1 of the present invention.

FIGS. 14A to 14G show X-ray photoelectron spectroscopy (XPS) profilesdepending on the depth of a charge generating junction layer.

FIG. 15 is a graph showing the electric conductivity of an air-annealedn-type semiconductor layer.

FIG. 16 shows the current efficiency-luminance characteristics and powerefficiency-luminance characteristics of a thin-film light-emittingdevice including a charge generating junction layer according to Example1 of the present invention.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present invention will now be described more fully with reference tothe accompanying drawings and contents disclosed in the drawings.However, the present invention should not be construed as limited to theexemplary embodiments described herein.

The terms used in the present specification are used to explain aspecific exemplary embodiment and not to limit the present inventiveconcept. Thus, the expression of singularity in the presentspecification includes the expression of plurality unless clearlyspecified otherwise in context. It will be further understood that theterms “comprise” and/or “comprising”, when used in this specification,specify the presence of stated components, steps, operations, and/orelements, but do not preclude the presence or addition of one or moreother components, steps, operations, and/or elements thereof.

It should not be understood that arbitrary aspects or designs disclosedin “embodiments”, “examples”, “aspects”, etc. used in the specificationare more satisfactory or advantageous than other aspects or designs.

In addition, the expression “or” means “inclusive or” rather than“exclusive or”. That is, unless otherwise mentioned or clearly inferredfrom context, the expression “x uses a or b” means any one of naturalinclusive permutations.

In addition, as used in the description of the disclosure and theappended claims, the singular form “a” or “an” is intended to includethe plural forms as well, unless context clearly indicates otherwise.

Although terms used in the specification are selected from termsgenerally used in related technical fields, other terms may be usedaccording to technical development and/or due to change, practices,priorities of technicians, etc. Therefore, it should not be understoodthat terms used below limit the technical spirit of the presentinvention, and it should be understood that the terms are exemplified todescribe embodiments of the present invention.

Also, some of the terms used herein may be arbitrarily chosen by thepresent applicant. In this case, these terms are defined in detailbelow. Accordingly, the specific terms used herein should be understoodbased on the unique meanings thereof and the whole context of thepresent invention.

Meanwhile, terms such as “first” and “second” are used herein merely todescribe a variety of constituent elements, but the constituent elementsare not limited by the terms. The terms are used only for the purpose ofdistinguishing one constituent element from another constituent element.

In addition, when an element such as a layer, a film, a region, and aconstituent is referred to as being “on” another element, the elementcan be directly on another element or an intervening element can bepresent.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art. It will be further understood that terms,such as those defined in commonly used dictionaries, should beinterpreted as having a meaning that is consistent with their meaning inthe context of the relevant art and the present invention, and will notbe interpreted in an idealized or overly formal sense unless expresslyso defined herein.

In addition, in the following description of the present invention, adetailed description of known functions and configurations incorporatedherein will be omitted when it may make the subject matter of thepresent invention unclear. The terms used in the specification aredefined in consideration of functions used in the present invention, andcan be changed according to the intent or conventionally used methods ofclients, operators, and users. Accordingly, definitions of the termsshould be understood on the basis of the entire description of thepresent specification.

Hereinafter, a thin-film light-emitting device including a chargegenerating junction layer according to embodiments of the presentinvention will be described with reference to FIGS. 1A to 2 .

FIG. 1A is the back-emitting structure of a thin-film light-emittingdevice including a charge generating junction layer according to oneembodiment of the present invention, and FIG. 1B is the top-emittingstructure of the thin-film light-emitting device including a chargegenerating junction layer according to one embodiment of the presentinvention. FIGS. 1A and 1B include the same configuration, and thus theconfiguration of the thin-film light-emitting device will be describedwith reference to FIG. 1A.

FIG. 1A is a cross-sectional view of a thin-film light-emitting deviceincluding a charge generating junction layer according to one embodimentof the present invention.

The thin-film light-emitting device including a charge generatingjunction layer according to one embodiment of the present inventionincludes a negative electrode 110, at least one light-emitting unit EU1formed on the negative electrode 110 and including a charge generatingjunction layer 121, an electron injection/transport layer 131, athin-film light-emitting layer 141, and a hole injection/transport layer151 in a sequential order, and a positive electrode 160 formed on thelight-emitting unit EU1.

The thin-film light-emitting device including a charge generatingjunction layer according to one embodiment of the present inventionincludes the negative electrode 110.

The negative electrode 110 itself may be used as a substrate and anelectrode, and may be formed using a material for forming the negativeelectrode 110 on a substrate.

The substrate is a base substrate for forming a light-emitting device.Substrates generally used in the art to which the present inventionpertains may be used as the substrate of the present invention. Inaddition, the material of the substrate is not particularly limited, andmay include silicon, glass, quartz, plastic, metal foil, and the like.

For example, the plastic substrate may include at least one ofpolyethylene terephthalate (PET), polyethylenenaphthelate (PEN),polypropylene (PP), polycarbonate (PC), polyimide (PI), tri acetylcellulose (TAC), and polyethersulfone (PES), and a flexible substratesuch as an aluminum foil or a stainless steel foil may be used as theplastic substrate.

The negative electrode 110 is an electrode for providing electrons to adevice, and a metal material, an ionized metal material, an alloymaterial, a metal ink material in a colloid state in a predeterminedliquid, and a transparent metal oxide may be used as the negativeelectrode 110.

As a specific example, the metal material may include at least one oflithium (Li), magnesium (Mg), aluminum (Al), aluminum-lithium (Al—Li),calcium (Ca), magnesium-indium (Mg—In), magnesium-silver (Mg—Ag),platinum (Pt), gold (Au), nickel (Ni), copper (Cu), barium (Ba), silver(Ag), indium (In), ruthenium (Ru), lead (Pd), rhodium (Rh), iridium(Ir), osmium (Os), and cesium (Cs). In addition, carbon (C), aconductive polymer, or a combination thereof may be used as the metalmaterial.

In addition, the transparent metal oxide may include at least one ofindium tin oxide (ITO), fluorine-doped tin oxide (FTO), antimony tinoxide (ATO), and aluminum-doped zinc oxide (AZO). In general, ITO isused as a material for forming a positive electrode, but in an invertedsolar cell structure, ITO may be used as a material for forming anegative electrode to form a transparent negative electrode. Thetransparent metal oxide electrode may be formed using a sol-gel, spraypyrolysis, sputtering, atomic layer deposition (ALD), or electron beamevaporation process.

The negative electrode 110 may be formed on the substrate by aconventional vacuum deposition process (e.g., chemical vapor deposition,CVD) or an application method in which printing is performed using pastemetal ink prepared by mixing metal flakes or metal particles and abinder, and any method capable of forming an electrode may be usedwithout being limited to the above methods.

At least one light-emitting unit EU1 including the charge generatingjunction layer 121, the thin-film light-emitting layer 141, and the holeinjection/transport layer 151 in a sequential order is formed on thenegative electrode 110.

The charge generating junction layer 121 has a pn junction structure inwhich a p-type semiconductor layer 121 a and an n-type semiconductorlayer 121 b are sequentially formed in a layer-by-layer structure.

Accordingly, tunneling of electrons from the highest occupied molecularorbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) mayoccur due to band bending. In the tunneling process, charge carriers(electrons or holes) are supplied to a thin-film light-emitting device.In the case of the first electron generating junction layer 121 on theside of the negative electrode 110, charge carriers supplied areelectrons.

In addition, formation of the charge generating junction layer 121 mayhave an effect similar to a case of containing a metal betweenelectrodes (negative and positive electrodes) in that the chargegenerating junction layer 121 supplies charge carriers.

Injection of electrons from the negative electrode 110 is criticallydependent on the work function of a material forming the negativeelectrode 110. Cleaning the negative electrode 110 or preparing thesurface of the negative electrode 110 before forming the negativeelectrode 110 may have a strong influence on the work function of thenegative electrode 110, and thus may have a strong influence on aninjection barrier.

The charge generating junction layer 121 separates the charge injectioncharacteristics of the thin-film light-emitting device from the workfunction of the negative electrode 110 to improve the charge injectioncharacteristics of the thin-film light-emitting device.

The charge generating junction layer 121 may be formed using a solutionprocess. Specifically, the charge generating junction layer 121 may beformed using any one solution process selected from spin coating, slitdye coating, ink-jet printing, spray coating, and dip coating.

Preferably, the charge generating junction layer 121 may be formed usingspin coating. In spin coating, a certain amount of a solution is droppedonto a substrate while rotating the substrate at high speed. At thistime, coating is performed by centrifugal force applied to the solution.

Since the charge generating junction layer 121 is formed using asolution process, a large area process may be performed, process timemay be shortened, and limitations on the semiconductor characteristicsof the upper and lower electrodes (positive and negative electrodes) maybe reduced.

The p-type and n-type semiconductor layers 121 a and 121 b constitutingthe charge generating junction layer 121 may be formed using oxidesemiconductors.

Accordingly, in the thin-film light-emitting device including a chargegenerating junction layer according to one embodiment of the presentinvention, the p-type and n-type semiconductor layers 121 a and 121 bare formed using oxide semiconductors, thereby increasing resistance tooxygen and moisture, and thus increasing the lifespan of the device.

The p-type semiconductor layer 121 a constituting the charge generatingjunction layer 121 may include one or more of copper oxide (CuO) andcopper oxide (CuO) doped with a first dopant, and the first dopant mayinclude one or more of nickel (Ni), copper (Cu), lithium (Li), and zinc(Zn).

A first dopant may be included in an amount of 0.1 atomic % to 50 atomic% in the copper oxide (CuO).

When the content of the first dopant is 0.1 atomic % or less, the effectof the dopant may be negligible due to too little content. When thecontent of the first dopant exceeds 50 atomic %, the characteristics ofthe p-type semiconductor layer may be degraded, thereby reducinggeneration of charge.

In addition, the p-type semiconductor layer 121 a may include one ormore of nickel oxide (NiO) and nickel oxide (NiO) doped with a seconddopant, and the second dopant may include one or more of tin (Sn),copper (Cu), lithium (Li), and zinc (Zn).

The second dopant may be included in an amount of 0.1 atomic % to 50atomic % in the nickel oxide (NiO).

When the content of the second dopant is 0.1 atomic % or less, theeffect of the dopant may be negligible due to too little content. Whenthe content of the second dopant exceeds 50 atomic %, thecharacteristics of the p-type semiconductor layer may be degraded,thereby reducing generation of charge.

The n-type semiconductor layer constituting the charge generatingjunction layer 121 may include one or more of zinc oxide (ZnO) and zincoxide (ZnO) doped with a third dopant. The third dopant may include oneor more of cesium (Cs), lithium (Li), aluminum (Al), magnesium (Mg),indium (In), calcium (Ca), and gallium (Ga).

The third dopant may be included in an amount of 0.1 atomic % to 20atomic % in the zinc oxide (ZnO).

When the content of the third dopant is 0.1 atomic % or less, the effectof the dopant may be negligible due to too little content. When thecontent of the third dopant exceeds 20 atomic %, the characteristics ofthe p-type semiconductor layer may be degraded, thereby reducinggeneration of charge.

The nickel oxide (NiO), copper oxide (CuO), and zinc oxide (ZnO)included in the charge generating junction layer 121 may be generated inthe form of at least one of sol-gel or nanoparticles.

In addition, in the thin-film light-emitting device including a chargegenerating junction layer according to one embodiment of the presentinvention, the n-type semiconductor layer 121 b is annealed.

The annealing treatment may be performed under an air or nitrogen (N₂)atmosphere. However, the present invention is not limited thereto, andthe annealing treatment may be performed under an inert gas atmosphereor under reduced pressure. In this case, the inert gas may include air,nitrogen (N₂), argon, neon, and helium.

The n-type semiconductor layer 121 b may serve as an electron generatinglayer or an electron transport layer depending on annealing treatmentenvironment. When annealing is performed under an air atmosphere, then-type semiconductor layer 121 b may serve as an electron generatinglayer. When heat treatment is performed under a nitrogen (N₂)atmosphere, the n-type semiconductor layer 121 b may serve as anelectron transport layer.

In the thin-film light-emitting device including a charge generatingjunction layer according to one embodiment of the present invention, byannealing the n-type semiconductor layer 121 b, the concentration ofoxygen vacancies at the interface between the p-type and n-typesemiconductor layers 121 a and 121 b may be adjusted.

Oxygen vacancies in a thin film may act as defects to trap holes orelectrons. Thus, charge generated at the junction of the p-type andn-type semiconductor layers 121 a and 121 b may also trapped in oxygenvacancies.

However, in the thin-film light-emitting device including a chargegenerating junction layer according to one embodiment of the presentinvention, when the n-type semiconductor layer 121 b is annealed, due toheat treatment in the air, oxygen penetrates into the interface betweenthe p-type and n-type semiconductor layers 121 a and 121 b, and oxygenvacancies at the interface are occupied with oxygen. As a result, theconcentration of the oxygen vacancies may be reduced, which affectsconductivity.

In addition, when the n-type semiconductor layer 121 b is heat-treatedin the air, oxygen penetrates, and oxygen vacancies are occupied withoxygen. Thus, as oxygen-hydrogen (O—H) bonds having a relatively lowbonding energy separate, the concentration of oxygen-hydrogen (O—H)decrease. Reduction in the concentration of oxygen-hydrogen (O—H)prevents trapping when electrons and holes recombine.

More specifically, in the thin-film light-emitting device including acharge generating junction layer according to one embodiment of thepresent invention, when the n-type semiconductor layer 121 b isannealed, oxygen vacancies induce charge trapping, and the concentrationof oxygen-hydrogen (O—H) at the interface between the p-type and n-typesemiconductor layers 121 a and 121 b is decreased, which inhibitstrapping of charge generated in the charge generating junction layer.

In addition, in the thin-film light-emitting device including a chargegenerating junction layer according to one embodiment of the presentinvention, when the n-type semiconductor layer 121 b is annealed, due toheat treatment in the air, the concentration ratio of a specificsemiconductor of the p-type semiconductor layer 121 a at the interfacebetween the p-type and n-type semiconductor layers 121 a and 121 b maybe selectively increased.

In the charge generating junction layer 121, the concentration ofmetal-oxygen (M-O) formed therein increases to contribute to chargegeneration. In the thin-film light-emitting device including a chargegenerating junction layer according to one embodiment of the presentinvention, the n-type semiconductor layer 121 b is annealed, whichincreases the proportion of the p-type semiconductor layer 121 a at theinterface between the p-type and n-type semiconductor layers 121 a and121 b. As a result, the concentration of metal-oxygen (M-O), e.g., Cu—O,at the interface between the p-type and n-type semiconductor layers 121a and 121 b increases, thereby further improving the charge generationefficiency of the charge generating junction layer 121.

The annealing treatment may be performed at a temperature of 160° C. to250° C. When the annealing temperature is less than 160° C., electricalproperties may deteriorate. When the annealing temperature exceeds 250°C., a lower thin film may deteriorate.

The annealing treatment may be performed under an air or nitrogen (N₂)atmosphere, and may be hot plate annealing, furnace annealing, or rapidthermal annealing (RTA). The rapid thermal annealing may include a gasrapid thermal annealing (GRTA) method using heated gas and a lamp rapidthermal annealing (LRTA) method using lamp light.

Preferably, in the thin-film light-emitting device including a chargegenerating junction layer according to one embodiment of the presentinvention, the temperature of a hot plate may be set to a desiredtemperature, the hot plate may be preheated for about 20 minutes, andheat treatment may be performed.

A light-emitting device has charge injection characteristics dependingon the work function of a metal. In the case of a light-emitting deviceincluding the charge generating junction layer 121 including only one ofthe p-type and n-type semiconductor layers 121 a and 121 b, due to anenergy bather by the work functions of upper and lower electrodes, aproblem rises in that injection of charge is not smooth.

However, in the case of the thin-film light-emitting device including acharge generating junction layer according to one embodiment of thepresent invention, by including the charge generating junction layer121, charge is generated at the interface between the p-type and n-typesemiconductor layers 121 a and 121 b. Thus, even when metals havingdifferent work functions are used as electrodes, the thin-filmlight-emitting device is not affected by the different work functions.Accordingly, in the case of the thin-film light-emitting deviceincluding a charge generating junction layer according to one embodimentof the present invention, since charge is generated at the interfacebetween the p-type and n-type semiconductor layers 121 a and 121 b bythe charge generating junction layer 121, generation and injection ofcharge may be stabilized.

The thickness of the p-type semiconductor layer 121 a may be 1 nm to 50nm. When the thickness of the p-type semiconductor layer 121 a is lessthan 1 nm, charge may not be generated, and charge tunneling may occur.When the thickness of the p-type semiconductor layer 121 a exceeds 50nm, the thickness of the device may increase, and thus the number ofpathways may increase, thereby degrading the characteristics of thedevice and increasing resistance.

The thickness of the n-type semiconductor layer 121 b may be 1 nm to 50nm. When the thickness of the n-type semiconductor layer 121 b is lessthan 1 nm, charge may not be generated. When the thickness of the n-typesemiconductor layer 121 b exceeds 50 nm, the thickness of a device mayincrease, and thus the number of pathways may increase, therebydegrading the characteristics of the device and increasing resistance.

Preferably, the thickness of the n-type semiconductor layer 121 b is 15nm. When the thickness of the n-type semiconductor layer 121 b is 15 nm,the charge generation rate may be increased, and the characteristics ofa thin-film light-emitting diode may be excellent.

More specifically, although the number of holes provided from thepositive electrode 160 is fixed, when the thickness of the n-typesemiconductor layer 121 b is minimized (i.e., 15 nm), generatedelectrons may have a short moving distance, trapping may be minimized,and thus efficient excitons may be generated. Accordingly, thecharacteristics of the thin-film light-emitting diode may be excellent.

The thickness ratio of the p-type semiconductor layer 121 a to then-type semiconductor layer 121 b may be 1:1 to 1:5.

When the thickness ratio of the p-type semiconductor layer 121 a to then-type semiconductor layer 121 b is within this range, holes andelectrons may be balanced, thereby improving the characteristics of thethin-film light-emitting diode.

The electron injection/transport layer 131 formed on the chargegenerating junction layer 121 serves to increase the efficiency of adevice by transporting electrons generated in the negative electrode 110to the thin-film light-emitting layer 141, and may be formed between thenegative electrode 110 and the thin-film light-emitting layer 141.

The electron injection/transport layer 131 may include at least one ofTiO₂, ZnO, SiO₂, SnO₂, WO₃, Ta₂O₃, BaTiO₃, BaZrO₃, ZrO₂, HfO₂, Al₂O₃,Y₂O₃, ZrSiO₄, SnO₂, TPBI, and TAZ.

The electron injection/transport layer 131 may be formed in the form ofa single layer, an electron injection layer and an electron transportlayer may be provided as separated layers, or only one of the electroninjection layer and the electron transport layer may be provided.

In the thin-film light-emitting layer 141, holes injected from thepositive electrode 160 and electrons injected from the negativeelectrode 110 meet to form excitons, and the formed excitons may be usedas a light-emitting layer that emits light having a specific wavelength.

The thin-film light-emitting layer 141 may include any one of quantumdots, an organic compound layer, an oxide layer, a nitride layer, asemiconductor layer, an inorganic compound layer, a phosphor layer, anda dye layer.

Preferably, the thin-film light-emitting layer 141 is a quantum dotlight-emitting layer including quantum dots or an organic light-emittinglayer including an organic compound. More preferably, the thin-filmlight-emitting layer 141 is a quantum dot light-emitting layer includingquantum dots.

As the quantum dot light-emitting layer, at least one selected from thegroup consisting of group II-VI semiconductor compounds, group III-Vsemiconductor compounds, group IV-VI semiconductor compounds, group IVelements or compounds, and combinations thereof may be used.

The group II-VI semiconductor compounds may include at least oneselected from the group consisting of binary compounds selected from thegroup consisting of CdSe, CdS, ZnS, CdTe, ZnSe, ZnTe, ZnO, HgS, HgSe,HgTe, and mixtures thereof; ternary compounds selected from the groupconsisting of CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe,HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe,HgZnTe, and mixtures thereof; and quaternary compounds selected from thegroup consisting of CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe,CdHgSTe, HgZnSeS, HgZnSeTe, HgZnSTe, and mixtures thereof.

The group III-V semiconductor compounds may include at least oneselected from the group consisting of binary compounds selected from thegroup consisting of GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN,InP, InAs, InSb, and mixtures thereof; ternary compounds selected fromthe group consisting of GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs,AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, GaAlNP, andmixtures thereof; and quaternary compounds selected from the groupconsisting of GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs,GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb,and mixtures thereof.

The group IV-VI semiconductor compounds may include at least oneselected from the group consisting of binary compounds selected from thegroup consisting of SnS, SnSe, SnTe, PbS, PbSe, PbTe, and mixturesthereof; ternary compounds selected from the group consisting of SnSeS,SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, and mixturesthereof; and quaternary compounds selected from the group consisting ofSnPbSSe, SnPbSeTe, SnPbSTe, and mixtures thereof.

The group IV elements or compounds may include at least one selectedfrom the group consisting of elemental compounds selected from the groupconsisting of Si, Ge, and mixtures thereof; and binary compoundsselected from the group consisting of SiC, SiGe, and mixtures thereof.

Preferably, CdSe/CdS/ZnS is used as the quantum dot light-emittinglayer.

The thin-film light-emitting layer 141 may be formed by vacuumdeposition, chemical vapor deposition, physical vapor deposition, atomiclayer deposition, metal organic chemical vapor deposition,plasma-enhanced chemical vapor deposition, molecular beam epitaxy,hydride vapor phase epitaxy, sputtering, spin coating, dip coating, andzone casting.

The hole injection/transport layer 151 is a layer for transporting andinjecting holes to the thin-film light-emitting layer 141, and may beformed by a vacuum deposition process or a solution process using anorganic material or an inorganic material.

The hole injection/transport layer 151 may be formed in the form of asingle layer, a hole injection layer and a hole transport layer may beprovided as separated layers, or only one of the hole injection layerand the hole transport layer may be provided.

The hole injection/transport layer 151 allows holes to be effectivelytransferred to the thin-film light-emitting layer 141, and may increaseluminous efficacy by balancing the densities of holes and electrons inthe thin-film light-emitting layer 141.

In addition, electrons injected from the negative electrode 110 to thethin-film light-emitting layer 141 are trapped in the thin-filmlight-emitting layer 141 by an energy barrier present at the interfacebetween the hole injection/transport layer 151 and the thin-filmlight-emitting layer 141. As a result, the probability of recombinationof electrons and holes increases, thereby improving luminous efficacy.

According to an embodiment, the hole injection/transport layer 151 maybe formed between the thin-film light-emitting layer 141 and the chargegenerating junction layer 121 or the auxiliary charge generatingjunction layer to further improve the effect of the charge generatingjunction layer 121 or the auxiliary charge generating junction layer.

The hole injection/transport layer 151 as a layer for transporting andinjecting holes may be formed using PEDOT:PSS. When the holeinjection/transport layer 151 is formed using PEDOT:PSS, additives suchas tungsten oxide, graphene oxide (GO), CNT, molybdenum oxide (MoOx),vanadium oxide (V₂O₅), and nickel oxide (NiOx) may be added. However,the present invention is not limited thereto, and various organic orinorganic materials may be used.

The thin-film light-emitting device may further include an auxiliarycharge generating junction layer on the light-emitting unit EU1.Accordingly, the auxiliary charge generating junction layer may beformed on the lower portion of the positive electrode 160, and theauxiliary charge generating junction layer may have a pn junctionstructure in which the p-type and n-type semiconductor layers aresequentially formed in a layer-by-layer structure.

According to an embodiment, the auxiliary charge generating junctionlayer may be formed using the same material and the same process as thecharge generating junction layer 121.

Accordingly, tunneling of electrons from the highest occupied molecularorbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) mayoccur due to band bending. In the tunneling process, charge carriers(electrons or holes) are supplied to a thin-film light-emitting device.In the case of a second charge generating layer on the side of thepositive electrode 160, charge carriers supplied are holes.

In addition, formation of the auxiliary charge generating junction layermay have an effect similar to a case of containing a metal betweenelectrodes (negative and positive electrodes) in that the auxiliarycharge generating junction layer supplies charge carriers.

Injection of holes from the positive electrode 160 is criticallydependent on the work function of a positive electrode material.Cleaning the positive electrode 160 or preparing the surface of thepositive electrode 160 before forming the positive electrode 160 mayhave a strong influence on the work function of the positive electrode160, and thus may have a strong influence on an injection barrier.

However, the auxiliary charge generating junction layer of the thin-filmlight-emitting device including a charge generating junction layeraccording to one embodiment of the present invention may separate thecharge injection characteristics of the thin-film light-emitting devicefrom the work function of the positive electrode 160 to improve thecharge injection characteristics of the thin-film light-emitting device.

In addition, the auxiliary charge generating junction layer 180 includesthe n-type semiconductor layer formed on the side of the positiveelectrode and the p-type semiconductor layer formed on the side of thethin-film light-emitting layer 141 to enable switching between holes fortransporting charge and electron transport.

The auxiliary charge generating junction layer may be formed using asolution process. Specifically, the auxiliary charge generating junctionlayer may be formed using any one solution process selected from spincoating, slit dye coating, ink-jet printing, spray coating, and dipcoating.

A light-emitting device has charge injection characteristics dependingon the work function of a metal. In the case of a light-emitting deviceincluding a charge injection layer including only one of p-type andn-type semiconductor layers, due to an energy bather by the workfunctions of upper and lower electrodes, a problem rises in thatinjection of charge is not smooth.

However, in the case of the thin-film light-emitting device including acharge generating junction layer according to one embodiment of thepresent invention, when the auxiliary charge generating junction layeris formed, charge is generated at the interface between the p-type andn-type semiconductor layers. Thus, even when metals having differentwork functions are used as electrodes, the thin-film light-emittingdevice is not affected by the different work functions. That is, sincecharge is generated at the interface between the p-type and n-typesemiconductor layers by a second charge generating junction layeraccording to one embodiment of the present invention, generation andinjection of charge may be stabilized.

In the thin-film light-emitting device including a charge generatingjunction layer according to one embodiment of the present invention, thelight-emitting unit may be repeatedly laminated 1 to 5 times.Accordingly, the thin-film light-emitting device including a chargegenerating junction layer according to one embodiment of the presentinvention may be formed in a tandem structure. The tandem structure ofthe thin-film light-emitting device including a charge generatingjunction layer according to one embodiment of the present invention willbe described in detail with reference to FIG. 2 .

On the light-emitting unit EU1, the positive electrode 160 is formed.

The positive electrode 160 is an electrode for providing holes to adevice, and may be formed by performing a solution process, such asscreen printing, on a transmissive electrode, a reflective electrode, ametal paste, or a metal ink material in a colloid state in apredetermined liquid.

The transmissive electrode material may include at least one of indiumtin oxide (ITO), indium zinc oxide (IZO), tin oxide (SnO₂), zinc oxide(ZnO), multilayer metal oxide/metal/metal oxide, graphene, and carbonnanotube, which are transparent and have excellent conductivity.

The reflective electrode material may include at least one of magnesium(Mg), aluminum (Al), silver (Ag), Ag/ITO, Ag/IZO, aluminum-lithium(Al—Li), calcium (Ca), magnesium-indium (Mg—In), and magnesium-silver(Mg—Ag).

The metal paste may include any one of silver paste (Ag paste), aluminumpaste (Al paste), gold paste (Au paste), and copper paste (Cu paste), ormay be an alloy thereof.

The metal ink material may include at least one of silver (Ag) ink,aluminum (Al) ink, gold (Au) ink, calcium (Ca) ink, magnesium (Mg) ink,lithium (Li) ink, and cesium (Cs) ink, and the metal material containedin the metal ink material may be ionized in the solution.

The positive electrode 160 may be formed on the substrate by aconventional vacuum deposition process (e.g., chemical vapor deposition,CVD) or an application method in which printing is performed using pastemetal ink prepared by mixing metal flakes or metal particles and abinder, and any method capable of forming an electrode may be usedwithout being limited to the above methods.

FIG. 1B is a cross-sectional view of a thin-film light-emitting deviceincluding a charge generating junction layer according to anotherembodiment of the present invention.

The thin-film light-emitting device according to another embodiment ofthe present invention includes the negative electrode 110, a reflectivelayer 170 formed on the negative electrode 110, at least onelight-emitting unit EU1 formed on the reflective layer and including thecharge generating junction layer 121, the electron injection/transportlayer 131, the thin-film light-emitting layer 141, and the holeinjection/transport layer 151 in a sequential order, the positiveelectrode 160 formed on the light-emitting unit EU1, and a refractiveindex compensation layer 180 formed on the positive electrode 160.

The negative electrode 110 is an electrode for providing electrons to adevice, and a metal material, an ionized metal material, an alloymaterial, a metal ink material in a colloid state in a predeterminedliquid, and a transparent metal oxide may be used as the negativeelectrode 110.

The thin-film light-emitting device includes the reflective layer 170formed on the negative electrode 110, and the reflective layer 170allows reflection from the negative electrode 110 to be easilyperformed. The reflective layer 170 may include at least one of silver(Ag), aluminum (Al), gold (Au), calcium (Ca), magnesium (Mg), lithium(Li), nickel (Ni), platinum (Pt), copper (Cu), and cesium (Cs).

At least one light-emitting unit EU1 including the charge generatingjunction layer 121, the thin-film light-emitting layer 141, and the holeinjection/transport layer 151 in a sequential order is formed on thereflective layer 170.

The charge generating junction layer 121 may have a pn junctionstructure in which the p-type and n-type semiconductor layers 121 a and121 b are sequentially formed in a layer-by-layer structure.

Accordingly, tunneling of electrons from the highest occupied molecularorbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) mayoccur due to band bending. In the tunneling process, charge carriers(electrons or holes) are supplied to a thin-film light-emitting device.In the case of the first electron generating junction layer 121 on theside of the negative electrode, charge carriers supplied are electrons.

In addition, by annealing the n-type semiconductor layer 121 b, theconcentration of oxygen vacancies at the interface between the p-typeand n-type semiconductor layers 121 a and 121 b may be adjusted.

The annealing treatment may be performed under an air or nitrogen (N₂)atmosphere.

When the n-type semiconductor layer 121 b is annealed, due to heattreatment in the air, the concentration of oxygen vacancies at theinterface between the p-type and n-type semiconductor layers 121 a and121 b may be reduced.

In addition, when the n-type semiconductor layer 121 b is annealed,oxygen vacancies that induce charge trapping decrease. As a result, theconcentration of oxygen-hydrogen (O—H) at the interface of the p-typeand n-type semiconductor layers 121 a and 121 b is reduced, therebypreventing generated charge from being re-trapped.

By increasing the concentration of metal-oxygen (M-O), charge generationefficiency may be improved. In addition, metal-oxygen (M-O) contributesto charge generation by improving semiconductor characteristics.

In addition, the annealing treatment may increase the proportion of thep-type semiconductor layer 121 a at the interface between the p-type andn-type semiconductor layers 121 a and 121 b.

When the n-type semiconductor layer 121 b is annealed, oxygenpenetrates, and the proportion of the p-type semiconductor layer 121 aat the interface between the p-type and n-type semiconductor layers 121a and 121 b may be increased.

For example, when copper oxide (CuO) is used as the p-type semiconductorlayer 121 a, when the n-type semiconductor layer 121 b is annealed,oxygen penetrates, and the number of Cu—O bonds at the interface betweenthe p-type and n-type semiconductor layers 121 a and 121 b may increase.

In addition, in the thin-film light-emitting device according to oneembodiment of the present invention, the surface roughness of the p-typesemiconductor layer 121 a may be decreased.

As a thin film is formed on the p-type semiconductor layer 121 a,roughness is generated on the surface of the p-type semiconductor layer121 a. When the surface roughness of the p-type semiconductor layer 121a increases, an electric field is not uniformly applied. As a result,the driving stability or lifespan of a device may reduce.

However, in the case of the thin-film light-emitting device according toone embodiment of the present invention, two layers, i.e., the p-typesemiconductor layer 121 a and the electron injection/transport layer 131are formed on the p-type semiconductor layer 121 a. Due to the presenceof the p-type semiconductor layer 121 a, roughness may be reduced,thereby stabilizing the driving of the device and increasing thelifespan of the device.

According to an embodiment, the n-type semiconductor layers 121 b in amulti-layer structure may be formed on the thin-film light-emittingdevice according to one embodiment of the present invention. In thiscase, due to the presence of the p-type semiconductor layers 121 a,roughness may be reduced, thereby stabilizing the driving of the deviceand increasing the lifespan of the device.

The positive electrode 160 is an electrode for providing holes to adevice, and a metal material, an ionized metal material, an alloymaterial, a metal ink material in a colloid state in a predeterminedliquid, and a transparent metal oxide may be used as the positiveelectrode 160.

The refractive index compensation layer 180 is formed on the positiveelectrode 160, and serves to adjust the refractive index between thepositive electrode 160 and the air. In addition, the refractive indexcompensation layer 180 may include at least one of SiO, SiO₂, Al₂O₃,BaO, MgO, HfO₂, ZrO₂, CaO₂, SrO₂, Y₂O₃, Si₃N₃, and AlN.

Light formed in the thin-film light-emitting layer 141 passes throughthe positive electrode 160 having a high refractive index, and thenpasses through the air having a low refractive index and the refractiveindex compensation layer 180. Then, light is efficiently emitted.

The refractive index compensation layer 180 has a refractive index valueof 0.5 to 4. When the refractive index value of the refractive indexcompensation layer 180 is less than 0.5, the refractive index of therefractive index compensation layer 180 and the refractive index of thepositive electrode 160 are so different that the refractive indexcompensation layer 180 may not serve to compensate for a refractiveindex. When the refractive index value of the refractive indexcompensation layer 180 exceeds 4, the refractive index of the refractiveindex compensation layer 180 and the refractive index of the air are sodifferent that the refractive index compensation layer 180 may not serveto compensate for a refractive index.

FIG. 2 illustrates the tandem structure of a thin-film light-emittingdevice according to one embodiment of the present invention.

Since the thin-film light-emitting device of a tandem structureincluding a charge generating junction layer according to one embodimentof the present invention includes the same components shown in FIG. 1Aor 1 b, detailed description of the same components will be omitted.

In FIG. 2 , a thin-film light-emitting device of a tandem structureincluding two light-emitting units is described, but the number of thelight-emitting units is not limited.

The thin-film light-emitting device of a tandem structure including acharge generating junction layer according to one embodiment of thepresent invention includes the negative electrode 110, one or morelight-emitting units EU1 and EU2 formed on the negative electrode 110and including charge generating junction layers 121 and 122, electroninjection/transport layers 131 and 132, thin-film light-emitting layers141 and 142, and hole injection/transport layers 151 and 152 in asequential order, and the positive electrode 160 formed on thelight-emitting units EU1 and EU2.

The light-emitting units EU1 and EU2 includes the first light-emittingunit EU1 including the first charge generating junction layer 121, thefirst electron injection/transport layer 131, the first thin-filmlight-emitting layer 141, and the first hole injection/transport layer151 in a sequential order and the second light-emitting unit EU2including the second charge generating junction layer 122, the secondelectron injection/transport layer 132, the second thin-filmlight-emitting layer 142, and the second hole injection/transport layer152 in a sequential order.

The number of lamination of the light-emitting units EU1 and EU2 is notparticularly limited. Preferably, the light-emitting units EU1 and EU2are repeatedly laminated 1 to 5 times.

When the light-emitting units EU1 and EU2 are laminated more than 5times, the same color may be repeatedly laminated to improve luminousefficacy. In addition, various colors may be laminated to fabricate adevice that emits white light.

The thin-film light-emitting device of a tandem structure including acharge generating junction layer according to one embodiment of thepresent invention is formed in a tandem structure in which thelight-emitting units EU1 and EU2 are laminated. Thus, a high-performancethin-film light-emitting device may be fabricated at low cost.

FIGS. 3A and 3B are flowcharts for explaining a method of fabricating athin-film light-emitting device including a charge generating junctionlayer according to one embodiment of the present invention.

Since the method of fabricating a thin-film light-emitting deviceincluding a charge generating junction layer according to one embodimentof the present invention shown in FIGS. 3A and 3B includes the samecomponents as the thin-film light-emitting device including a chargegenerating junction layer according to one embodiment of the presentinvention shown in FIG. 1A, description of the same components will beomitted.

In addition, the thin-film light-emitting device including a chargegenerating junction layer according to another embodiment of the presentinvention (FIG. 1B) and the thin-film light-emitting device of a tandemstructure including a charge generating junction layer according to oneembodiment of the present invention (FIG. 2 ) may be fabricated bychanging the order of the method of fabricating a thin-filmlight-emitting device including a charge generating junction layeraccording to one embodiment of the present invention shown in FIGS. 3Aand 3B.

The method of fabricating a thin-film light-emitting device including acharge generating junction layer according to one embodiment of thepresent invention includes step S110 of forming a negative electrode ona substrate, step S120 of forming at least one light-emitting unit onthe negative electrode, and step S130 of forming a positive electrode onthe light-emitting unit.

In addition, step S120 of forming at least one light-emitting unitincludes step S121 of forming a charge generating junction layer on thenegative electrode, step S122 of forming an electron injection/transportlayer on the charge generating junction layer, step S123 of forming athin-film light-emitting layer on the electron injection/transportlayer, and step S124 of forming a hole injection/transport layer on thethin-film light-emitting layer.

In the method of fabricating a thin-film light-emitting device includinga charge generating junction layer according to one embodiment of thepresent invention, in step S110, the negative electrode is formed on thesubstrate.

Then, in step S120, the charge generating junction layer is formed onthe negative electrode.

The negative electrode itself may be used as a substrate and anelectrode, and may be formed using a material for forming a negativeelectrode on a substrate.

The substrate is a base substrate for forming a light-emitting device.Substrates generally used in the art to which the present inventionpertains may be used as the substrate of the present invention. Inaddition, the material of the substrate is not particularly limited, andmay include silicon, glass, plastic, metal foil, and the like.

The negative electrode is an electrode for providing electrons to adevice, and a metal material, an ionized metal material, an alloymaterial, a metal ink material in a colloid state in a predeterminedliquid, and a transparent metal oxide may be used as the negativeelectrode.

The negative electrode may be formed on the substrate by a conventionalvacuum deposition process (e.g., chemical vapor deposition, CVD) or anapplication method in which printing is performed using paste metal inkprepared by mixing metal flakes or metal particles and a binder, and anymethod capable of forming an electrode may be used without being limitedto the above methods.

Step S120 includes step S121 of forming a charge generating junctionlayer on the negative electrode, step S122 of forming an electroninjection/transport layer on the charge generating junction layer, stepS123 of forming a thin-film light-emitting layer on the electroninjection/transport layer, and step S124 of forming a holeinjection/transport layer on the thin-film light-emitting layer.

In step S121, the charge generating junction layer is formed on thenegative electrode.

The charge generating junction layer may have a layer-by-layer structurein which the p-type and n-type semiconductor layers are formed, and maybe formed using a solution process.

More specifically, step S121 includes a step of forming the p-typesemiconductor layer on the negative electrode, a step of forming then-type semiconductor layer on the p-type semiconductor layer, and a stepof annealing the n-type semiconductor layer.

The p-type and n-type semiconductor layers may be formed using asolution process. Accordingly, a large area process may be performed,process time may be shortened, and limitations on the semiconductorcharacteristics of the upper and lower electrodes (positive and negativeelectrodes) may be reduced.

Specifically, the p-type and n-type semiconductor layers may be formedusing any one solution process selected from spin coating, slit dyecoating, ink-jet printing, spray coating, and dip coating.

Preferably, the p-type and n-type semiconductor layers may be formedusing spin coating. In spin coating, a certain amount of a solution isdropped onto a substrate while rotating the substrate at high speed. Atthis time, coating is performed by centrifugal force applied to thesolution.

Since the charge generating junction layer (p-type and n-typesemiconductor layers) is formed using a solution process, a large areaprocess may be performed, process time may be shortened, and limitationson the semiconductor characteristics of the upper and lower electrodes(positive and negative electrodes) may be reduced.

In addition, in the method of fabricating a thin-film light-emittingdevice including a charge generating junction layer according to oneembodiment of the present invention, the n-type semiconductor layer 121b is annealed.

The annealing treatment may be performed under an air or nitrogen (N₂)atmosphere. However, the present invention is not limited thereto, andthe annealing treatment may be performed under an inert gas atmosphereor under reduced pressure. In this case, the inert gas may include air,nitrogen (N₂), argon, neon, and helium.

By annealing the n-type semiconductor layer, the concentration of oxygenvacancies at the interface between the p-type and n-type semiconductorlayers may be adjusted. More specifically, when the n-type semiconductorlayer is annealed, due to heat treatment in the air, the concentrationof oxygen vacancies at the interface between the p-type and n-typesemiconductor layers may be reduced.

In addition, when the n-type semiconductor layer 121 b is annealed,dehydration or dehydrogenation of the charge generating junction layermay occur. In this case, dehydration or dehydrogenation means removal ofH, OH, and the like in addition to H₂.

More specifically, according to the method of fabricating a thin-filmlight-emitting device including a charge generating junction layeraccording to one embodiment of the present invention, when the n-typesemiconductor layer is annealed, oxygen vacancies induce chargetrapping, and the concentration of oxygen-hydrogen (O—H) at theinterface between the p-type and n-type semiconductor layers isdecreased, which inhibits generated charge from being re-trapped.

Accordingly, when an excess of hydrogen (including water or hydroxylgroups) is removed by dehydration or dehydrogenation, the structure ofthe charge generating junction layer may be aligned, and an impuritylevel in an energy gap may be reduced.

In addition, when the n-type semiconductor layer 121 b is annealed,oxygen penetrates, and as a result, the proportion of the p-typesemiconductor layer at the interface between the p-type and n-typesemiconductor layers may be increased.

In the charge generating junction layer, semiconductor characteristicsare improved by metal-oxygen (M-O) formed therein, which contributes tocharge generation. In the thin-film light-emitting device including acharge generating junction layer according to one embodiment of thepresent invention, the n-type semiconductor layer is annealed, whichincreases the proportion of the p-type semiconductor layer at theinterface between the p-type and n-type semiconductor layers. As aresult, the concentration of metal-oxygen (M-O), e.g., Cu—O, at theinterface between the p-type and n-type semiconductor layers isincreased, thereby further improving the charge generation efficiency ofthe charge generating junction layer 121.

The annealing treatment may be performed at a temperature of 160° C. to250° C. When the annealing temperature is less than 160° C., resistancemay increase. When the annealing temperature exceeds 250° C., a lowerthin film may deteriorate.

The annealing treatment may be performed under an air or nitrogen (N₂)atmosphere, and may be hot plate annealing, furnace annealing, or rapidthermal annealing (RTA). The rapid thermal annealing may include a gasrapid thermal annealing (GRTA) method using heated gas and a lamp rapidthermal annealing (LRTA) method using lamp light.

Preferably, according to the method of fabricating a thin-filmlight-emitting device including a charge generating junction layeraccording to one embodiment of the present invention, the temperature ofa hot plate may be set to a desired temperature, the hot plate may bepreheated for about 20 minutes, and heat treatment may be performed.

The p-type and n-type semiconductor layers constituting the chargegenerating junction layer may be formed using oxide semiconductors.Thus, resistance to oxygen and moisture may be improved, therebyincreasing the lifespan of a device.

Then, in step S122, the electron injection/transport layer is formed onthe charge generating junction layer.

The electron injection/transport layer may include at least one of TiO₂,ZnO, SiO₂, SnO₂, WO₃, Ta₂O₃, BaTiO₃, BaZrO₃, ZrO₂, HfO₂, Al₂O₃, Y₂O₃,ZrSiO₄, SnO₂, TPBI, and TAZ.

The electron injection/transport layer may be formed using at least oneof vacuum deposition, chemical vapor deposition, physical vapordeposition, atomic layer deposition, metal organic chemical vapordeposition, plasma-enhanced chemical vapor deposition, molecular beamepitaxy, hydride vapor phase epitaxy, sputtering, spin coating, dipcoating, and zone casting.

Then, in step S123, the thin-film light-emitting layer is formed.

The thin-film light-emitting layer may be a quantum dot light-emittinglayer or an organic light-emitting layer. Preferably, the thin-filmlight-emitting layer is a quantum dot light-emitting layer.

As the quantum dot light-emitting layer, at least one selected from thegroup consisting of group II-VI semiconductor compounds, group III-Vsemiconductor compounds, group IV-VI semiconductor compounds, group IVelements or compounds, and combinations thereof may be used.

The thin-film light-emitting layer may be formed using vacuumdeposition, chemical vapor deposition, physical vapor deposition, atomiclayer deposition, metal organic chemical vapor deposition,plasma-enhanced chemical vapor deposition, molecular beam epitaxy,hydride vapor phase epitaxy, sputtering, spin coating, dip coating, orzone casting.

Then, in step S124, the hole injection/transport layer is formed on thethin-film light-emitting layer.

The hole injection/transport layer as a layer for transporting andinjecting holes may be formed using PEDOT:PSS. When the holeinjection/transport layer is formed using PEDOT:PSS, additives such astungsten oxide, graphene oxide (GO), CNT, molybdenum oxide (MoOx),vanadium oxide (V₂O₅), and nickel oxide (NiOx) may be added. However,the present invention is not limited thereto, and various organic orinorganic materials may be used.

The hole injection/transport layer may be formed using at least one ofvacuum deposition, chemical vapor deposition, physical vapor deposition,atomic layer deposition, metal organic chemical vapor deposition,plasma-enhanced chemical vapor deposition, molecular beam epitaxy,hydride vapor phase epitaxy, sputtering, spin coating, dip coating, andzone casting.

Finally, in step S130, the positive electrode is formed on thelight-emitting unit.

The positive electrode is an electrode for providing holes to a device,and may be formed by performing a solution process, such as screenprinting, on a transmissive electrode, a reflective electrode, a metalpaste, or a metal ink material in a colloid state in a predeterminedliquid.

The positive electrode may be formed on the substrate by a conventionalvacuum deposition process (e.g., chemical vapor deposition, CVD) or anapplication method in which printing is performed using paste metal inkprepared by mixing metal flakes or metal particles and a binder, and anymethod capable of forming an electrode may be used without being limitedto the above methods.

According to an embodiment, after step S120, a step of forming anauxiliary charge generating junction layer on the light-emitting unitmay be further included.

The auxiliary charge generating junction layer may be formed using thesame material and method as the above-described charge generatingjunction layer.

The auxiliary charge generating junction layer may have a layer-by-layerstructure in which the p-type and n-type semiconductor layers areformed, and may be formed using a solution process.

The auxiliary charge generating junction layer may be formed using asolution process. Accordingly, a large area process may be performed,process time may be shortened, and limitations on the semiconductorcharacteristics of the upper and lower electrodes (positive and negativeelectrodes) may be reduced.

Specifically, the p-type and n-type semiconductor layers may be formedusing any one solution process selected from spin coating, slit dyecoating, ink-jet printing, spray coating, and dip coating.

Preferably, the p-type and n-type semiconductor layers may be formedusing a spin coating. In spin coating, a certain amount of a solution isdropped onto a substrate while rotating the substrate at high speed. Atthis time, coating is performed by centrifugal force applied to thesolution.

Since the auxiliary charge generating junction layer (p-type and n-typesemiconductor layers) is formed using a solution process, a large areaprocess may be performed, process time may be shortened, and limitationson the semiconductor characteristics of the upper and lower electrodes(positive and negative electrodes) may be reduced.

In addition, the n-type semiconductor layer 121 b may be annealed. Theannealing treatment may be performed under an air or nitrogen (N₂)atmosphere. However, the present invention is not limited thereto, andthe annealing treatment may be performed under an inert gas atmosphereor under reduced pressure. In this case, the inert gas may include air,nitrogen (N₂), argon, neon, and helium.

The annealing treatment may be performed under an air or nitrogen (N₂)atmosphere, and may be hot plate annealing, furnace annealing, or rapidthermal annealing (RTA). The rapid thermal annealing may include a gasrapid thermal annealing (GRTA) method using heated gas and a lamp rapidthermal annealing (LRTA) method using lamp light.

Preferably, in the thin-film light-emitting device including a chargegenerating junction layer according to one embodiment of the presentinvention, the temperature of a hot plate may be set to a desiredtemperature, the hot plate may be preheated for about 20 minutes, andheat treatment may be performed.

Hereinafter, the electrical or optical characteristics of the thin-filmlight-emitting device including a charge generating junction layeraccording to embodiments of the present invention will be described withreference to FIGS. 4A to 16 .

Fabrication Examples Comparative Example

A negative electrode was formed on a glass substrate, and then 2 at %Li-doped ZnO for injecting electrons was formed in a thickness of 50 nmon the negative electrode. A thin-film light-emitting layer was formedin a thickness of 30 nm on the formed electron injection layer usingspin coating, a hole transport layer was formed in a thickness of 20 nmon the thin-film light-emitting layer using spin coating, and PEDOT:PSSfor injecting holes was formed in a thickness of 20 nm on the holetransport layer using spin coating. Then, to form a positive electrodeon the hole injection layer, aluminum (Al) was deposited on the holeinjection layer using a vacuum deposition method.

Example 1

A solution prepared by adding Li:CuO prepared by doping 20 atomic % Lion copper oxide and Li:ZnO prepared by doping 10 atomic % Li on zincoxide into ethanol as a solvent was printed on a negative electrodeformed of ITO under an air atmosphere using a solution process to form alayer-by-layer structure including 20 atomic % Li:CuO and 10 atomic %Li:ZnO. Then, 10 atomic % Li:ZnO was annealed on a hot plate at 250° C.for 10 minutes to form a charge generating junction layer in a thicknessof 15 nm.

Thereafter, an electron transport layer of 10 atomic % Li:ZnO was formedin a thickness of 15 nm using a printing method, and a quantum dotlight-emitting layer of a CdSe/CdS/ZnS (core/shell/shell type) structurewas formed in a thickness of 30 to 40 nm using a printing method. Then,holes transport layers of 4,4,4-tris(Ncarbazolyl) triphenylamine (TCTA)and 4,4′-bis[N-(naphthyl)-Nphenylamino] biphenyl (NPB) were formed usinga vacuum deposition method in thicknesses of 10 nm and 20 nm,respectively. Then, HAT-CN as a hole injection layer was formed in athickness of 20 nm using a vacuum deposition method, and a positiveelectrode of Al was formed in a thickness of 100 nm using a vacuumdeposition method to fabricate a thin-film light-emitting device.

FIGS. 4A to 4H show the characteristics of a thin-film light-emittingdevice (control device) that does not include a solution process-basedcharge generating junction layer according to Comparative Example andthe characteristics of a thin-film light-emitting device including acharge generating junction layer (CGL device) according to Example 1 ofthe present invention.

FIG. 4A shows the band diagram of the thin-film light-emitting deviceaccording to Comparative Example that does not include a solutionprocess-based charge generating junction layer, and FIG. 4B shows theband diagram of the thin-film light-emitting device including a chargegenerating junction layer according to Example 1 of the presentinvention.

FIG. 4C shows current density-voltage (J-V) characteristics, FIG. 4Dshows luminance-voltage (L-V) characteristics, FIG. 4E shows currentefficiency-luminance (C/E-L) characteristics, and FIG. 4F shows powerefficiency-luminance (P/E-L) characteristics.

FIGS. 4G and 4H show the histograms of the maximum values of the currentefficiency and power efficiency of a thin-film light-emitting deviceincluding a charge generating junction layer (CGL device) according toExample 1 of the present invention.

In FIGS. 4G and 4H, 18 devices were measured in five batches of thethin-film light-emitting device including a charge generating junctionlayer (CGL device) according to Example 1 of the present invention.

In Table 1 below, the detailed characteristics of FIGS. 4C to 4F areshown.

TABLE 1 @ 1,000 cd/m2 @ 10,000 cd/m2 VT VD C/Emax P/Emax C/E P/E C/E P/EQLED (V) (V) (cd/A) (lm/W) (cd/A) (lm/W) (cd/A) (lm/W) Comparative 2.75.8 34.9 32.4 30.4 16.4 16.3 6.0 Example Example 2.8 6.4 35.4 33.5 27.813.6 14.0 4.5

In Table 1, VT represents a voltage when light having an intensity of 1cd/m² is emitted, VD represents a voltage when light having an intensityof 1,000 cd/m² is emitted, C/E represents current efficiency, i.e., theamount of light generated by a current of 1 A, P/E represents powerefficiency, i.e., the amount of light generated by a power of 1 W,C/Emax represents the maximum efficiency of C/E, and P/Emax representsthe maximum efficiency of P/E.

Referring to FIGS. 4A to 4H and Table 1, the thin-film light-emittingdevice including a charge generating junction layer (CGL device)according to Example 1 of the present invention includes a solutionprocess-based charge generating junction layer. Thus, compared toComparative Example, the thin-film light-emitting device of Example 1has improved current density-voltage characteristics, luminance-voltagecharacteristics, current efficiency-luminance characteristics, and powerefficiency-luminance characteristics.

FIGS. 5A to 5D show the characteristics of a thin-film light-emittingdevice including a charge generating junction layer according to Example1 of the present invention depending on the dopant concentrations of ap-type semiconductor layer.

FIG. 5A shows current density-voltage characteristics, FIG. 5B showsluminance-voltage characteristics, FIG. 5C shows currentefficiency-luminance characteristics, and FIG. 5D shows powerefficiency-luminance characteristics.

In FIGS. 5A to 5D, a solution process-based CuO was used as a p-typesemiconductor layer, and characteristics were measured depending ondifferent doping concentrations of Li (0 at %, 5 at %, 10 at %, 20 at %,and 40 at %).

In Table 2, the detailed characteristics of FIGS. 5A to 5D are shown.

TABLE 2 Li doping @ 1,000 cd/m2 @ 10,000 cd/m2 concentration VT VDC/Emax P/Emax C/E P/E C/E P/E in CuO (V) (V) (cd/A) (lm/W) (cd/A) (lm/W)(cd/A) (lm/W) 0% (CuO) 3.0 7.3 31.4 27.9 25.3 10.9 12.2 3.5  5 at % 2.97.0 32.8 29.8 25.9 11.5 12.7 3.7 10 at % 3.2 8.1 30.9 25.1 24.4 9.4 12.53.3 20 at % 3.1 7.0 30.8 26.2 25.2 11.3 12.6 3.9 40 at % 2.9 7.2 26.222.8 17.1 7.5 7.2 2.1

Referring to FIGS. 5A to 5D and Table 2, it can be seen that, dependingon the dopant concentrations of the p-type semiconductor layer, thecurrent density-voltage characteristics, luminance-voltagecharacteristics, current efficiency-luminance characteristics, and powerefficiency-luminance characteristics of the thin-film light-emittingdevice including a charge generating junction layer according to Example1 of the present invention are adjusted, and the best characteristicsare exhibited when the concentration of a dopant included in the p-typesemiconductor layer is 10 at %.

FIGS. 6A to 6D show the characteristics of a thin-film light-emittingdevice including a charge generating junction layer according to Example1 of the present invention depending on the annealing temperatures of ann-type semiconductor layer.

FIG. 6A shows current density-voltage characteristics, FIG. 6B showsluminance-voltage characteristics, FIG. 6C shows currentefficiency-luminance characteristics, and FIG. 6D shows powerefficiency-luminance characteristics.

In FIGS. 6A to 6D, a solution process-based LZO was used as an n-typesemiconductor layer, and characteristics were measured depending ondifferent annealing temperatures (160° C., 190° C., 220° C., and 250°C.).

In Table 3, the detailed characteristics of FIGS. 6A to 6D are shown.

TABLE 3 @ 1,000 cd/m2 @ 10,000 cd/m2 LZO annealing VT VD C/Emax P/EmaxC/E P/E C/E P/E tem (° C.) (V) (V) (cd/A) (lm/W) (cd/A) (lm/W) (cd/A)(lm/W) 160 3.1 11.2 27.6 18.7 20.4 5.7 10.8 2.4 190 2.6 6.8 25.4 20.222.8 10.5 11.7 3.5 220 2.6 6.3 27.1 22.2 25.1 12.6 13.6 4.4 250 2.7 6.227.9 17.2 20.4 10.3 9.5 3.0

Referring to FIGS. 6A to 6D and Table 3, it can be seen that, dependingon annealing temperatures, the current density-voltage characteristics,luminance-voltage characteristics, current efficiency-luminancecharacteristics, and power efficiency-luminance characteristics of thethin-film light-emitting device including a charge generating junctionlayer according to Example 1 of the present invention are adjusted, andthe characteristics of a device (diode) are best improved when theannealing temperature of LZO, which is an n-type semiconductor layer, is220° C. or more.

FIGS. 7A to 7D show the characteristics of a thin-film light-emittingdevice including a charge generating junction layer according to Example1 of the present invention depending on the thicknesses of an n-typesemiconductor layer.

FIG. 7A shows current density-voltage characteristics, FIG. 7B showsluminance-voltage characteristics, FIG. 7C shows currentefficiency-luminance characteristics, and FIG. 7D shows powerefficiency-luminance characteristics.

In FIGS. 7A to 7D, a solution process-based LZO was used as an n-typesemiconductor layer, and characteristics were measured depending ondifferent thicknesses (15 nm, 25 nm, 35 nm, and 50 nm).

In Table 4, the detailed characteristics of FIGS. 7A to 7D are shown.

TABLE 4 @ 1,000 cd/m2 @ 10,000 cd/m2 LZO thickness VT VD C/Emax P/EmaxC/E P/E C/E P/E (nm) (V) (V) (cd/A) (lm/W) (cd/A) (lm/W) (cd/A) (lm/W)15 2.7 6.3 29.1 28.6 22.4 11.2 11.0 3.4 25 2.8 6.5 28.1 24.6 23.4 11.411.4 3.6 35 3.0 9.3 21.5 17.4 16.6 5.6 8.4 1.8 50 2.9 7.3 20.9 17.4 17.17.4 8.1 2.2

Referring to FIG. 7A to FIG. 7D and Table 4, it can be seen that,depending on the thicknesses of the n-type semiconductor layer, thecurrent density-voltage characteristics, luminance-voltagecharacteristics, current efficiency-luminance characteristics, and powerefficiency-luminance characteristics of the thin-film light-emittingdevice including a charge generating junction layer according to Example1 of the present invention are adjusted, and the characteristics of adevice (diode) are best improved when the thickness of LZO, which is ann-type semiconductor layer, is 15 nm.

FIGS. 8A to 8D show the characteristics of a thin-film light-emittingdevice including a charge generating junction layer according to Example1 of the present invention depending on the thicknesses of an electroninjection/transport layer formed on the upper portion of a solutionprocess-based charge generating junction layer.

FIG. 8A shows current density-voltage characteristics, FIG. 8 b showsluminance-voltage characteristics, FIG. 8C shows currentefficiency-luminance characteristics, and FIG. 8D shows powerefficiency-luminance characteristics.

In Table 5, the detailed characteristics of FIGS. 8A to 8D are shown.

TABLE 5 Electron @ 1,000 cd/m2 @ 10,000 cd/m2 transport layer VT VDC/Emax P/Emax C/E P/E C/E P/E thickness (nm) (V) (V) (cd/A) (lm/W)(cd/A) (lm/W) (cd/A) (lm/W) 15 2.8 6.4 35.4 33.5 27.8 13.6 14.0 4.5 252.7 6.3 29.1 28.6 22.4 11.2 11.0 3.4 35 2.8 7.2 20.8 19.0 15.2 6.6 6.21.6

Referring to FIGS. 8A to 8D and Table 5, it can be seen that, dependingon the thicknesses of the electron injection/transport layer, thecurrent density-voltage characteristics, luminance-voltagecharacteristics, current efficiency-luminance characteristics, and powerefficiency-luminance characteristics of the thin-film light-emittingdevice including a charge generating junction layer according to Example1 of the present invention are adjusted, and the characteristics of adevice (diode) is best improved when the thickness of the electroninjection/transport layer is 15 nm.

FIGS. 9A to 9C show the characteristics of a thin-film light-emittingdevice (w/o) that does not include an n-type semiconductor layer and thecharacteristics of a thin-film light-emitting device (w/) including acharge generating junction layer according to Example 1 of the presentinvention.

FIG. 9A shows current density-voltage characteristics, FIG. 9B showsluminance-voltage characteristics, FIG. 9C shows currentefficiency-luminance characteristics.

In Table 6, the detailed characteristics of FIGS. 9A to 9C are shown.

TABLE 6 N-type oxide @ 1,000 cd/m2 @ 10,000 cd/m2 semiconductor VT VDC/Emax P/Emax C/E P/E C/E P/E with/without LZO (V) (V) (cd/A) (lm/W)(cd/A) (lm/W) (cd/A) (lm/W) Absence 7.4 — 10.4 3.3 — — — — Presence 2.76.2 21.9 17.2 20.4 10.3 9.5 3.0

Referring to FIGS. 9A to 9C and Table 6, it can be seen that, comparedto the thin-film light-emitting device (w/o) that does not include ann-type semiconductor layer, the current density-voltage characteristics,luminance-voltage characteristics, current efficiency-luminancecharacteristics, and power efficiency-luminance characteristics of thethin-film light-emitting device (w/) including a charge generatingjunction layer according to Example 1 of the present invention areimproved, and device characteristics are improved.

FIG. 10 is a graph showing the current-voltage characteristics of athin-film light-emitting device (PP:WOx/LZO CGJ) including a chargegenerating junction layer consisting of a p-type semiconductor layerincluding an organic substance and an n-type semiconductor layerincluding an oxide semiconductor and the current-voltage characteristicsof a thin-film light-emitting device (Li:CuO/LZO CGJ) including a chargegenerating junction layer according to Example 1 of the presentinvention.

Referring to FIG. 10 , compared to the thin-film light-emitting deviceincluding a charge generating junction layer consisting of a p-typesemiconductor layer including an organic substance and an n-typesemiconductor layer including an oxide semiconductor, the amount ofcurrent flowing through the thin-film light-emitting device including acharge generating junction layer according to Example 1 of the presentinvention is larger, indicating that the characteristics of a device aresignificantly improved.

FIGS. 11A to 11C show the characteristics of a top-emitting thin-filmlight-emitting device (a thin-film light-emitting device including acharge generating junction layer according to another embodiment of thepresent invention).

FIG. 11A shows current density-voltage characteristics (Current Density)and luminance-voltage characteristics (Luminance), FIG. 11B show CIEcolor coordinates, and FIG. 9C shows the luminous image of atop-emitting thin-film light-emitting device.

Referring to FIGS. 11A to 11C, it can be seen that the current densityand luminance of the top-emitting thin-film light-emitting device (athin-film light-emitting device including a charge generating junctionlayer according to another embodiment of the present invention) aresignificantly improved.

FIGS. 12A to 12F show the ultraviolet photoelectron spectroscopy spectraof a thin-film light-emitting device including a charge generatingjunction layer according to Example 1 of the present invention.

FIG. 12A shows the band diagram of the thin-film light-emitting deviceincluding a charge generating junction layer according to Example 1 ofthe present invention that includes a green quantum dot light-emittinglayer, FIG. 12B shows secondary-electron cutoff regions, FIG. 12C showsthe Fermi-edge regions of a UV/O₃-treated positive electrode, FIG. 12Dshows the Fermi-edge regions of a UV/O₃-treated p-type semiconductorlayer, FIG. 12E shows the Fermi-edge regions of a UV/O₃-treated n-typesemiconductor layer, and FIG. 12F is the Fermi-edge regions of aUV/O₃-treated green quantum dot light-emitting layer.

In FIGS. 12A to 12F, the work functions of the positive electrode, thep-type semiconductor layer, the n-type semiconductor layer, and thegreen quantum dot light-emitting layer are calculated to be 4.60 eV,4.29 eV, 2.95 eV, and 2.90 eV from secondary-electron cutoff regions,respectively.

Referring to FIGS. 12A to 12F, it can be seen that energy levels changeas each layer is laminated.

FIGS. 13A to 13D show the characteristics of a thin-film light-emittingdevice including an NPD/HAT-CN junction as a charge generating junctionlayer and the characteristics of a thin-film light-emitting deviceincluding a charge generating junction layer (Li:CuO/LiZnO) according toExample 1 of the present invention.

FIG. 13A shows the band diagram of the thin-film light-emitting deviceincluding an NPD/HAT-CN junction as a charge generating junction layer,FIG. 13B shows the band diagram of the thin-film light-emitting deviceincluding a charge generating junction layer according to Example 1 ofthe present invention, FIG. 13C shows current density-voltagecharacteristics, and FIG. 13D shows relative charge generationefficiency.

The relative charge generation efficiency may be calculated by Equation1 below.

$\begin{matrix}{{{Relative}{CGE}(\%)} = {\frac{{{{Abs}\left( {{Reverse}J} \right)}{at}V} = {{- 3}V}}{{{{Abs}\left( {{Forward}J} \right)}{at}V} = {{+ 3}V}} \times 100{(\%).}}} & \left\lbrack {{Equation}1} \right\rbrack\end{matrix}$

The relative charge generation efficiency of the thin-filmlight-emitting device including an NPD/HAT-CN junction as a chargegenerating junction layer is 67% at −3 V, and the relative chargegeneration efficiency of the thin-film light-emitting device including acharge generating junction layer according to Example 1 of the presentinvention is 83% at −3 V, indicating that relative charge generationefficiency is significantly improved.

In addition, referring to FIGS. 13A to 13D, in the case of the thin-filmlight-emitting device including a charge generating junction layeraccording to Example 1 of the present invention, air annealing of then-type semiconductor layer reduces oxygen vacancies in a metal oxide,thereby improving the electrical and optical characteristics of adevice.

FIGS. 14A to 14G show X-ray photoelectron spectroscopy (XPS) profilesdepending on the depth of a charge generating junction layer.

FIG. 14A shows the measurement points (P1, P2, P3, and P4) of the chargegenerating junction layer of the thin-film light-emitting deviceincluding a charge generating junction layer according to Example 1 ofthe present invention, FIGS. 14B to 14D show the depth profiles ofelements constituting a charge generating junction layer when annealingis performed under a nitrogen (N₂) atmosphere, and FIGS. 14E to 14G showthe depth profiles of elements constituting a charge generating junctionlayer when annealing is performed under an air atmosphere.

In X-ray photoelectron spectroscopy, when annealing is performed underan air or nitrogen atmosphere at the measurement points (P1, P2, P3, andP4) of the charge generating junction layer, the concentration of oxygenvacancies and the concentration of oxygen-hydrogen (O—H) may beconfirmed.

Referring to FIGS. 14A to 14G, it can be seen that, when annealing isperformed under an air or nitrogen atmosphere, oxygen vacancies inducecharge trapping, and the concentrations of oxygen vacancies at P1 to P3(the interface between n-type and p-type semiconductor layers) and theconcentration of oxygen-hydrogen (O—H) gradually decrease, and theconcentration of M-O increases.

Since the concentration of M-O contributes to charge generation, whenannealing is performed under an air or nitrogen atmosphere, theefficiency of the charge generating junction layer may further improved.

In addition, it can be seen that, when annealing is performed under anair or nitrogen atmosphere, the surface roughness of the p-typesemiconductor layer is reduced.

FIG. 15 is a graph showing the electric conductivity of an air-annealedn-type semiconductor layer.

Measurement is performed on electron-only-devices (EODs) including aLi:ZnO layer having a thickness of 150 nm.

Referring to FIG. 15 , it can be seen that Li:ZnO annealed at 250° C.exhibits 500 time higher electrical conductivity than Li:ZnO annealed at160° C.

FIG. 16 shows the current efficiency-luminance characteristics and powerefficiency-luminance characteristics of a thin-film light-emittingdevice including a charge generating junction layer according to Example1 of the present invention.

Referring to FIG. 16 , it can be seen that, in terms of luminance, thecurrent efficiency and power efficiency of the thin-film light-emittingdevice including a charge generating junction layer according to Example1 of the present invention are improved.

Although the present invention has been described through limitedexamples and figures, the present invention is not intended to belimited to the examples. Those skilled in the art will appreciate thatvarious modifications, additions, and substitutions are possible,without departing from the scope and spirit of the invention.

Therefore, the scope of the present invention should not be limited bythe embodiments, but should be determined by the following claims andequivalents to the following claims.

What is claimed is:
 1. A method of fabricating a thin-filmlight-emitting device, comprising: a step of forming a negativeelectrode on a substrate; a step of forming at least one light-emittingunit on the negative electrode; and a step of forming a positiveelectrode on the light-emitting unit, wherein the step of forming thelight-emitting unit comprises a step of forming a charge generatingjunction layer on the negative electrode; a step of forming an electroninjection/transport layer on the charge generating junction layer; astep of forming a thin-film light-emitting layer on the electroninjection/transport layer; and a step of forming a holeinjection/transport layer on the thin-film light-emitting layer, whereinthe charge generating junction layer has a layer-by-layer structure inwhich a p-type semiconductor layer and an n-type semiconductor layer areformed, and a concentration of oxygen vacancies at an interface betweenthe p-type and n-type semiconductor layers is adjusted by annealing then-type semiconductor layer, wherein the annealing treatment increases aproportion of the p-type semiconductor layer at the interface betweenthe p-type and n-type semiconductor layers.
 2. The method according toclaim 1, wherein the charge generating junction layer is formed using asolution process, wherein the annealing treatment is performed at atemperature of 160° C. to 250° C., and wherein the method furthercomprises, after the step of forming the light-emitting unit, a step offorming an auxiliary charge generating junction layer on thelight-emitting unit.